KOCH, Robert (1843—). A German physician and bacteriologist, born at Clausthal, Hanover. He studied medicine at Göttingen; then practiced medicine in Langenhagen, Rackwitz, and Wollstein. It was at Wollstein, from 1872 to 1880, that he began the researches in bacteriology upon which his fame chiefly rests. Koch's researches on the history of anthrax were published in 1876, and two years later followed his study on the history of traumatic infective diseases. These works placed bacteriology upon a firm scientific basis. Appointed in 1880 a member of the Imperial Board of Health in Berlin, he continued the unwearied study of the communicable causes of anthrax, cholera, and tuberculosis, isolating the tubercle bacillus in 1882. To do this it was necessary to invent new appliances for microscopical work, and new methods of staining specimens to render visible these special microorganisms. In this way Koch set on foot advances in bacteriology which are of inestimable value.

Koch and his supporters have shown that many diseases are caused by specific germs. In experiments upon animals Koch discovered that the injection of diseased blood produced septicæmia in house-mice, discovering also that the microörganisms found in the blood of these animals were identical in form and character with those in the blood used for injection. At the site of the injection of the infected fluid abscesses developed. The pus from those abscesses, full of the bacteria when injected in a diluted form into a healthy animal, invariably produced the disease. Koch produced erysipelas in the same way. The infectious character of tuberculosis of the lungs had been suspected for many years, but to him belongs the credit of discovering its specific germ. The tubercle bacilli are distinguished from others by marked characteristics, and are present in all cases of the disease. Koch demonstrated these bacteria in the sputum of those suffering from pulmonary tuberculosis. In 1883 Koch became chief of the German commission sent to Egypt and India to investigate cholera, with the result of discovering the cholera spirillum or comma bacillus. In the same year Koch published a method of inoculation to prevent anthrax. Returning to Germany in 1884, Koch received 100,000 marks from the Government. In 1885 he was appointed professor in the University of Berlin and director of the new Hygienic Institute. In November, 1890, through the premature report by a student, it became generally known that Dr. Koch had discovered and tested, by a series of careful experiments, a compound substance which, when administered by injection hypodermically, was destructive of the tubercle bacilli, and hence presumably a swift and certain cure for tuberculosis. The excitement throughout the world attendant upon this announcement was very great. Physicians from all countries flocked to Berlin, and consumptive patients traveled thither in the hope of certain cure. Amid all this clamor, Koch remained for a long time silent as to the method of preparing the ‘lymph,’ and singularly conservative in the claims that he made of its efficacy. In January, 1891, he put forth a statement concerning the nature of his lymph, which, while not giving all the details of its preparation, made it evident that it was itself prepared from the bacilli. The essential parts of his statement will be found in the article Tuberculin. The lymph, or, as ho preferred to call it, the paratoloid, is a poison and must be used with great caution. The reaction consequent upon its use is so marked as to lead many physicians to doubt its ultimate advantages. Professor Billroth stated that with three patients the reactions seemed so dangerous as to force him to discontinue the treatment; and Schrötter of Vienna (January, 1891) and Crocq of Brussels confirm this statement from their own experience. The value of this discovery as a means of cure in the human race must therefore be regarded as yet in doubt, though the German Government began erecting the Koch Institute for Consumptives with an immense laboratory and 150 beds.

In 1901, before the British Congress on Tuberculosis held in London, Koch called attention to the fact that even at his first publication of the ætiology of tuberculosis, he expressed himself with reserve regarding the identity of the disease in man and animals, announcing his belief that bovine tuberculosis and human tuberculosis were distinctly different diseases. These statements, at the time characterized as sensational, gave rise to extensive disputation and experiment. Among Koch's published works are: ZurAetiologie des Milzbrandes (1876); Untersuchungenüber die Aetiologie derWundinfektionskrankheiten (1878; Eng. trans. by Cheyne, 1880); Ueber die Milzbrandimpfung. Eine Entgegnung aufden von Pasteur in Genf gehaltenen Vortrag (1882); Beitrag zur Aetiologie der Tuberculose (1882; Eng. trans. by Boyd, 1886); Ueber dieCholerabakterien (1884; Eng. trans, by Laycock, 1886); Ueber Naturheilung und medizinischeKunst (1885); On Disinfection, abstracted andtranslated by Whitelegge (1886); WeitereMitteilungen über ein Heilmittel gegen Tuberculose (1890); Ueber bakteriologische Forschung (1890; trans. into English 1891); Ergebnisse der vomDeutschen Reich ausgesandten Malaria-Expeditionen (1900); An Investigation of PathogenicOrganisms, translated by Horsley (1886); Aerztliche Beobachtungen in den Tropen (1898); Diagnosis, Treatment, and Prophylaxis of TropicalMalaria, translated by Shakespeare (1898). See the articles on Tuberculosis and Tuberculin.